Various types of data transceivers, circuits or devices made to send and receive data, are generally known in the art. One type of data transceiver is a differential voltage transceiver. Differential voltage transceivers operate by providing a voltage difference over two conductors such that the data transceiver that receives the differential voltage signal can sense the differential voltage between the two conductors and assign a data value according to the differential voltage. Differential data transceivers send and receive data in a variety of applications such as point-of-sale terminals, factory automation, and automotive electronics. Certain standards control the communication protocols for different types of differential data transceivers, for example, the EIA-422 (RS-422), the ANSI TIA/EIA-485-A (RS-485), universal serial bus (USB), and IEC 11898-2 (CAN) standards. Each of these standards assigns logic values based on the threshold(s) of voltage sensed on the differential voltage line. If the differential voltage is above the threshold, for example, the assigned value is one state, and if the differential voltage is below the threshold, the assigned value is another state. Typically, a gray area of differential voltage range exists around the threshold(s) to account for noise and other tolerances.
During field installation of equipment using differential signaling, one common fault is the reversal of the two wires that carry the differential voltage. With existing transceivers, such an installation error causes data errors and/or complete communication stoppage because the received signals do not correspond to the intended or expected signal ranges. In many applications, this reversed wire fault is not detected until after installation of the system is complete, and correction of the miswiring is costly or impractical.
For example, in the RS-485 standard if the differential voltage on the wires carrying the signal is positive, the state is called “on” or binary logic zero. If the differential voltage is negative, the state is called “off” or binary logic one. If the differential voltage is near zero, the state is not defined. Should the signaling wires be reversed, however, the signals as received by the transceiver would be exactly reversed. In other words, the receiver would see a differential voltage that is positive when the intended signal is that the differential voltage is negative. Accordingly, the entire transmission for an RS-485 standard system will be reversed when wires are misconnected—all the zeros will be interpreted as ones and all the ones will be interpreted as zeros.
In another example, in a controller area network (CAN) differential driver standard circuit, if the differential voltages are positive the state is called “dominant,” and if the differential voltage is near zero, the state is called “recessive”. If the differential voltage is negative, the state is not defined or it may be interpreted as recessive. Thus, in CAN standard transceivers, the transmitted differential voltage signal is either positive or near zero. In the case of a reversed wire situation, however, the receiver will nearly only see negative signals or signals near zero. Accordingly, the receiver will only ever see a recessive state and never see a dominant state.